Hello, rockstarbookschi. 

I'll clarify the details about the invoice changes on the payment link. 

Yes, that's correct. As what AlexV mentioned, changes to your invoices will always sync on the payment link. We're also unable to add a PDF version of the link. 

Though, your customer won't be able to see any changes if they look at the original email body (not the payment link itself). 

Our developers might add a way to let you send a payment link as a PDF (without syncing the changes). I would recommend sending feedback by clicking the gear icon, then selecting Feedback. 

For reference about creating invoices, you can check this article: Create invoices in QuickBooks Online. 

Need help categorizing your income and expense bank transactions? This article can help you with the process: Categorize and match online bank transactions in QuickBooks Online.

If you need to learn more about processing invoices and payments in QuickBooks, please let me know. I'd be happy to address your concerns. If you want to complete other tasks, lay down the details and I'll help you out.